In a normal, healthy heart, cardiac contraction is initiated by the spontaneous excitation of the sinoatrial (“SA”) node, located in the right atrium. The electrical impulse generated by the SA node travels to the atrioventricular (“AV”) node where it is transmitted to the bundle of His and Purkinje network, which branches in many directions to facilitate simultaneous contraction of the left and right ventricles.
In certain disease states, the heart's ability to pace properly is compromised. Currently, such dysfunction is commonly rectified by the implantation of implantable pacemakers. While improving the lives of many patients, implantable pacemakers have a limited lifetime and hence, may expose a patient to multiple surgeries to replace the implantable pacemaker. Moreover, implantable pacemakers may not be capable of directly responding to the body's endogenous signaling that interacts with the SA node to increase or decrease its pacing rate.
Recently, biological methods of influencing the pacing rate of cardiac cells have been developed, including the use of various drugs and pharmaceutical compositions. Developments in genetic engineering have resulted in methods for genetically modifying cardiac cells to influence their intrinsic pacing rate. For example, U.S. Pat. No. 6,214,620 describes a method for suppressing excitability of ventricular cells by overexpressing (e.g. K+ channels) or underexpressing certain ion channels (e.g. Na+ and Ca2+ channels). PCT Publication No. WO 02/087419 describes methods and systems for modulating electrical behavior of cardiac cells by genetic modification of inwardly rectifying K+ channels (IK1) in quiescent ventricular cells. PCT Publication No. WO 02/098286 describes methods for regulating pacemaker function of cardiac cells with HCN molecules (HCN 1, 2, 3, or 4 isoforms of the pacemaker current If).
A need remains, however, to implement a system of genetic modification therapy (biopacing) in cooperation with an implantable medical device (IMD) to insure successful curative therapy for cardiac dysfunction.